Interaction of low density lipoproteins with human aortic elastin

Lipid Indices, Elastin Turnover and the Development of Microvascular Complications – A Study in Diabetic Patients with Arterial Hypertension

Background and Aims: An important factor in the development of vascular wall lesions is the degradation of the elastic fiber major protein – elastin. Elastin peptides (EDP) derived from this degradation are present in the circulation and are a stimulus for the production of anti-elastin antibodies (AEAbs) IgM, IgG and IgA. The aim of this study was to investigate the possible association between AEAbs, lipid indices and the development of microvascular complications.

Material and Methods: Sera of 93 patients with type 2 diabetes mellitus (T2DM) and arterial hypertension (AH) were investigated (mean age 61,4 ± 11,3 years, diabetes duration 9,88 ± 3,12 years; hypertension duration 9,28 ± 4,98). ELISA was used for determination of anti-elastin antibodies. These levels were compared to serum AEAbs in 42 age- and sex-matched controls. Diabetic patients were divided in two groups according to the presence – Group 1 (n = 67) or absence – Group 2 (n = 26) of microangiopathy. The lipid profile and lipid indices (log TG/HDL, LDL/HDL, TC/HDL and TG/HDL) were also studied.

Results: Patients with T2DM and AH showed statistically significant higher levels of serum AEAbs IgA than healthy controls – 0,338 (0,133÷0,452) vs. 0,006 (0,052÷0,068) (KW = 19,54; P < 0.0001). Group 1 showed statistically significant higher levels of AEAbs IgA than patients without microangiopathy – 0,353 (0,173÷0,471) vs. 0,235 (0,098÷0,377) (KW = 3,36; p = 0.05) and healthy controls – 0,353 (0,173÷0,471) vs. 0,006 (0,052÷0,068) (KW = 20,37; p < 0,0001) (0.37 ± 0,03 vs. 0.06÷0.01) (p = 0.0001). Patients from Group 2 showed significantly higher levels of AEAbs IgA than controls 0,235 (0,098÷0,377) vs. 0,006 (0,052÷0,068) (KW = 8,54; P = 0.003). AEAbs IgA showed correlation with insulin dose (r = −0.35); (p = 0.01), SBP (r = 0.31); (p = 0.001), HbA1c (r = 0.21); (p = 0.04), BMI (r = 0.22); (p = 0.01). AEAbs IgA correlated with log TG/HDL (r = 0.28); (p = 0.001), LDL/HDL (r = 0.22); (p = 0.01) TC/HDL (r = 0.22); (p = 0.01) and with TG/HDL (r = 0.15); (p = 0.05).

Conclusion: Our study proved a relationship between elevation of AEAb IgA, high lipid indices and the development of microvascular complications in patients with type 2 diabetes mellitus and arterial hypertension.

Circulating Anti-Elastin Antibody Levels and Arterial Disease Characteristics: Associations with Arterial Stiffness and Atherosclerosis

PURPOSE

Elastin is a major arterial structural protein, and elastin-derived peptides are related to arterial change. We previously reported on a novel assay developed using aortic elastin peptides; however, its clinical implications remain unclear. In this study, we assessed whether anti-elastin antibody titers reflect the risk of coronary artery disease (CAD) or its characteristics.

MATERIALS AND METHODS

We included 174 CAD patients and 171 age- and sex-matched controls. Anti-elastin antibody titers were quantified by enzyme-linked immunosorbent assay. Parameters of arterial stiffness, including the augmentation index (AI) and heart-to-femoral pulse wave velocity (hfPWV), were measured non-invasively. The clinical and angiographic characteristics of CAD patients were also evaluated. Associations between anti-elastin levels and vascular characteristics were examined by linear regression analysis.

RESULTS

The median blood level of anti-elastin was significantly lower in the CAD group than in the controls [197 arbitrary unit (a.u.) vs. 63 a.u., p<0.001]. Levels of anti-elastin were significantly lower in men and in subjects with hypertension, diabetes mellitus, hyperlipidemia, or high hfPWV. Nevertheless, anti-elastin levels were not dependent on atherothrombotic events or the angiographic severity of CAD. In a multivariate analysis, male sex (β=-0.38, p<0.001), diabetes mellitus (β=-0.62, p<0.001), hyperlipidemia (β=-0.29, p<0.001), and AI (β=-0.006, p=0.02) were ultimately identified as determinants of anti-elastin levels.

CONCLUSION

Lower levels of anti-elastin are related to CAD. The association between antibody titers and CAD is linked to arterial stiffness rather than the advancement of atherosclerosis.

Cardiomyocyte intracellular cholesteryl ester accumulation promotes tropoelastin physical alteration and degradation: Role of LRP1 and cathepsin S

Dyslipemia has a direct impact on cardiac remodeling by altering extracellular matrix (ECM) components. One of the main ECM components is elastin, a proteic three-dimensional network that can be efficiently degraded by cysteine proteases or cathepsins. Dyslipemic status in insulin resistance and combined hyperlipoproteinemia diseases include raised levels of very low density lipoproteins (VLDL), triglyceride (TG)-cholesteryl ester (CE)-rich lipoproteins. Enhanced VLDL concentration promotes cardiomyocyte intracellular cholesteryl ester (CE) accumulation in a LRP1-dependent manner. The aim of this work was to analyze the effect of cardiomyocyte intracellular CE accumulation on tropoelastin (TE) characteristics and to investigate the role of LRP1 and cathepsin S (CatS) on these effects. Molecular studies showed that LRP1 deficiency impaired CE selective uptake and accumulation from TG-CE-rich lipoproteins (VLDL+IDL) and CE-rich lipoproteins (aggregated LDL, agLDL). Biochemical and confocal microscopic studies showed that LRP1-mediated intracellular CE accumulation increased CatS mature protein levels and induced an altered intracellular TE globule structure. Biophysical studies evidenced that LRP1-mediated intracellular CE accumulation caused a significant drop of Tg2 glass transition temperature of cardiomyocyte secreted TE. Moreover, CatS deficiency prevented the alterations in TE intracellular globule structure and on TE glass transition temperature. These results demonstrate that LRP1-mediated cardiomyocyte intracellular CE accumulation alters the structural and physical characteristics of secreted TE through an increase in CatS mature protein levels. Therefore, the modulation of LRP1-mediated intracellular CE accumulation in cardiomyocytes could impact pathological ventricular remodeling associated with insulin-resistance and combined hyperlipoproteinemia, pathologies characterized by enhanced concentrations of TG-CE-rich lipoproteins.

ABCC6- a new player in cellular cholesterol and lipoprotein metabolism?

BACKGROUND

Dysregulations in cholesterol and lipid metabolism have been linked to human diseases like hypercholesterolemia, atherosclerosis or the metabolic syndrome. Many ABC transporters are involved in trafficking of metabolites derived from these pathways. Pseudoxanthoma elasticum (PXE), an autosomal-recessive disease caused by ABCC6 mutations, is characterized by atherogenesis and soft tissue calcification.

METHODS

In this study we investigated the regulation of cholesterol biosynthesis in human dermal fibroblasts from PXE patients and healthy controls.

RESULTS

Gene expression analysis of 84 targets indicated dysregulations in cholesterol metabolism in PXE fibroblasts. Transcript levels of ABCC6 were strongly increased in lipoprotein-deficient serum (LPDS) and under serum starvation in healthy controls. For the first time, increased HMG CoA reductase activities were found in PXE fibroblasts. We further observed strongly elevated transcript and protein levels for the proprotein convertase subtilisin/kexin type 9 (PCSK9), as well as a significant reduction in APOE mRNA expression in PXE.

CONCLUSION

Increased cholesterol biosynthesis, elevated PCSK9 levels and reduced APOE mRNA expression newly found in PXE fibroblasts could enforce atherogenesis and cardiovascular risk in PXE patients. Moreover, the increase in ABCC6 expression accompanied by the induction of cholesterol biosynthesis supposes a functional role for ABCC6 in human lipoprotein and cholesterol homeostasis.

Lipid loading of human vascular smooth muscle cells induces changes in tropoelastin protein levels and physical structure

Aggregated low-density lipoprotein (agLDL), one of the main LDL modifications in the arterial intima, contributes to massive intracellular cholesteryl ester (CE) accumulation in human vascular smooth muscle cells (VSMC), which are major producers of elastin in the vascular wall. Our aim was to analyze the levels, physical structure, and molecular mobility of tropoelastin produced by agLDL-loaded human VSMC (agLDL-VSMC) versus that produced by control VSMC. Western blot analysis demonstrated that agLDL reduced VSMC-tropoelastin protein levels by increasing its degradation rate. Moreover, our results demonstrated increased levels of precursor and mature forms of cathepsin S in agLDL-VSMC. Fourier transform infrared analysis revealed modifications in the secondary structures of tropoelastin produced by lipid-loaded VSMCs. Thermal and dielectric analyses showed that agLDL-VSMC tropoelastin has decreased glass transition temperatures and distinct chain dynamics that, in addition to a loss of thermal stability, lead to strong changes in its mechanical properties. In conclusion, agLDL lipid loading of human vascular cells leads to an increase in cathepsin S production concomitantly with a decrease in cellular tropoelastin protein levels and dramatic changes in secreted tropoelastin physical structure. Therefore, VSMC-lipid loading likely determines alterations in the mechanical properties of the vascular wall and plays a crucial role in elastin loss during atherosclerosis.

Age-related changes in human macular Bruch's membrane as seen by quick-freeze/deep-etch

Lipid-containing inclusions have been observed in human Bruch's membrane (BrM) and are postulated to be associated with age-related maculopathy (ARM), a major cause of legal blindness in developed countries. The dehydration associated with specimen preparation for thin-section transmission electron microscopy causes loss of these inclusions. Better preservation of the ultrastructure of the inclusions and tissue is achieved by using a quick-freeze/deep-etch preparation. We use this technique to examine normal human macular BrM in order to characterize the deposition of the lipid-rich inclusions and their age-related accumulation within different layers of the tissue. We find that various inclusions mentioned in other studies can be formed by combinations of three basic structures: lipoprotein-like particles (LLPs), small granules (SGs) and membrane-like structures. These inclusions are associated with collagen and elastic fibrils by fine filaments. In younger eyes, these inclusions are found mostly in the elastic (EL) and outer collageneous layer (OCL) and occupy a small fraction of the interfibrillar spacing. As age increases, LLPs and SGs gradually fill the interfibrillar spacing of the EL and inner collageneous layer (ICL) of the tissue, and later form a new sublayer, the lipid wall, within the boundary region between the basal lamina of retinal pigment epithelium (RPE) and ICL. Because the formation of the lipid wall only occurs after these inclusions fill the ICL, and it seems unlikely that the LLPs can pass through the packed layer, this result suggests a possible RPE origin of the LLPs that make up the lipid wall.

Structure of large arteries: Orientation of elastin in rabbit aortic internal elastic lamina and in the elastic lamellae of aortic media

This study was designed to further our understanding of the elastic ultrastructure of vessels. Scanning electron microscopy and transmission electron microscopy were used to study the histomorphologic properties of the elastic fibers of rabbit aorta after purification of the elastin by means of hot alkaline treatments. The elastic fibers of whole rabbit aorta samples were also studied using confocal microscopy. Morphological assessment revealed that the elastin fibers contained in the elastic lamellae of media are perpendicular to the blood flow, and that the elastic fibers of the internal elastic lamina are parallel to the luminal flow. In conclusion, the structure of the elastin making up the elastic lamellae of the media is oriented in such a way as to sustain the circumferential mechanical stress of pulsation. By contrast, the structure of the elastin fibers that make up the internal elastic lamina provides little mechanical support for the circumferential tension, but can support longitudinal loading and act as a fenestrated membrane.

Serum fibrillin-antifibrillin immune complexes among diabetic children

The fibrillins are large glycoproteins components of 10-nm microfibrils found in the extracellular matrix of most tissues. Microfibrils play a role in elastic fiber assembly and serve to link cells to elastic fibers in the extracellular matrix. Fibrillin-1 (FBN-1) and -2 (FBN-2) are large, secreted glycoproteins known to be components of extracellular matrix microfibrils located in the vasculature, basement membrane, and various connective tissues and are often associated with a superstructure known as the elastic fiber. Anti-fibrillin antibodies found in some autoimmune diseases could form circulating immune complexes (CIC) with corresponding antigens. Type 1 (insulin-dependent) diabetes mellitus is an autoimmune disease leading to formation of different types of autoantibodies. To determine the possible presence of FBN-anti-FBN CIC (IgG and IgM) were studied by modified version of ELISA 35 children with Type 1 diabetes mellitus (mean age--12.37+/-3.77 years, diabetes duration 4+/-3.5 years). Eight of the diabetics had vascular complications. Twenty healthy children (mean age--11.58+/-2.89 years) were used as controls. Diabetics showed statistically significant higher levels of FBN-anti-FBN-2 CIC - IgG (0.303+/-0.076 vs. 0.252+/-0.029; p=0.029) and IgM (0.415+/-0.085 vs. 0.348+/-0.069; p=0.018) compared to the control group. FBN-anti-FBN-1 CIC IgM correlate with diabetes duration (r=0.52; p=0.0015) and BMI (r=0.33, p=0.053) while FBN-anti-FBN-1 CIC IgG correlate with serum Zinc (r=0.49, p=0.006). FBN-anti-FBN-2 CIC IgG correlate with microalbuminuria (r=0.65, p=0.0046) and retinopathy (r=0.61, p=0.0001). This study suggests that there may be a relationship of levels of FBN-anti-FBN-2 CIC IgG with the development of diabetic microangiopathy. Of course the number of the tested patients is limited for definitive conclusions. Although the meaning of these results is still being determined, the measurement of FBN-anti-FBN CIC may represent immunologic markers of FBN metabolism.

Absence of the protease inhibitor cystatin C in inflammatory cells results in larger plaque area in plaque regression of apoE-deficient mice

Matrix remodelling plays an important role in regulating plaque stability. Cystatin C, an inhibitor of the elastin-degrading cysteine proteases of the cathepsin family, is believed to be one of the key protease inhibitors in this process. The aim of the present study was to investigate the role of leukocyte-specific cystatin C expression under conditions that favour plaque regression. Apolipoprotein E-deficient mice (apoE-/-) were given a Western-type diet 15 weeks prior transplantation with bone marrow from mice lacking cystatin C (cysC-/-) or cystatin C positive (cysC+/+) mice, in both cases apoE+/+ to create conditions favouring plaque regression. Transplantations were verified with PCR and Western analyses. Transplanted mice showed a 70% decrease in lipid content and reduction in plaque area compared to baseline ApoE-/- mice, demonstrating plaque regression due to apoE expression in macrophages. apoE-/- mice transplanted with cysC-/- bone marrow were then compared to mice transplanted with cysC+/+ bone marrow. Mice receiving cysC-/- bone marrow had a 30% larger plaque area, despite absence of significant differences in plasma cholesterol and lipid contents in plaque. Unexpectedly, mice transplanted with cystatin C-deficient bone marrow cells had increased elastin and collagen content in lesions. These observations suggest that leukocyte-specific expression of cystatin C is actively involved in matrix remodelling associated with plaque regression.

Detection of Free Antielastin Antibodies among Diabetic Children

Antibodies to elastin breakdown products are found in the serum of all human subjects and correlate with their respective serum peptide levels. The presence of these antielastin antibodies (AEAbs) and the corresponding antigens in circulation leads to the formation of circulating immune complexes (CICs). The aim of this study was to determine if the serum levels of free AEAbs (not bound in CICs) correlate with the development of vascular complications in diabetic children. To this end, we used a method for detecting immune complexes (complement inhibition factor [CIF]-enzyme-linked immunosorbent assay [ELISA]) in combination with an ELISA for detection of AEAbs. The levels of free immunoglobulin G (IgG) AEAbs were studied in the sera of 54 diabetic children (mean age 12.3+/-4 years; diabetes duration 5.2+/-3.7 years). Thirty-two of the children had vascular complications (group 1), and 22 were without vascular complications (group 2). Twenty healthy children (mean age 13.6+/-4.2 years) were used as controls. The diabetics showed statistically significant higher levels of free AEAbs (0.490 E492+/-0.244 E492 vs 0.307 E492+/-0.081 E492; p = .02) compared with the control group. In group 1, free AEAbs showed statistically significant higher levels than controls (0.523+/-0.269 vs 0.307+/-0.081; p = .016). Eighteen of 54 (33%) patients were positive for free AEAbs (13 of 32 [41%] in group 1 and 5 of 22 [22%] in group 2). Free AEAb levels in all diabetics showed a correlation with systolic blood pressure (r = .44; p = .01), diastolic blood pressure (r = .46; p = .009), total cholesterol (r = .33; p = .05), triglycerides (r= .38; p = .03), high-density lipoprotein (r= -.46; p = .009), serum fructose (r= .43; p = .001), and microalbuminuria (r= .41; p = .002). Patients who had vascular pathology showed a correlation of free AEAbs with microalbuminuria (r= .434; p= .026), serum fructose (r= .63; p = .0004), hemoglobin A1c (r= .392; p = .043), and triglycerides (r= .456; p = .025). These findings suggest that elevated levels of free IgG AEAbs are associated with the development of diabetic vascular complications in children.

Normal and oxidized low density lipoproteins accumulate deep in physiologically thickened intima of human coronary arteries

Diffuse intimal thickening (DIT) that develops as a physiologic adaptation in the arterial wall has been implicated to have a predilection for atherosclerosis. We histologically investigated the lipid accumulation process in the human coronary DIT by focusing on the localization of normal and oxidized low-density lipoproteins (LDLs). Immunohistochemistry for apolipoprotein B 100 (a major apolipoprotein of LDL) and 8-iso-prostaglandin F(2alpha) (an oxidative product in LDL) showed substantial accumulation of oxidized relative to normal LDLs in the deep layers of DIT (52/139 segments). Subendothelial deposition of normal rather than oxidized LDLs, known as an early event of fatty streak formation, was less frequently found (13/139 segments). In contrast with fibrofatty lesions, lipid accumulation localized deep in DIT was characterized by fine lipid droplets scattered in the preserved tissue and by its association with neither macrophage accumulation nor apoptosis in the constituent cells. On the other hand, the deep intimal location of lipid accumulation clearly coincided with increased type I and type III collagen and elastic fibers but rarely with sulfated proteoglycans including decorin, which were all strongly expressed in advanced lesions. This lipid accumulation was found only in sites with DIT of more than 200 micro m, occasionally extending to the inner media and involving neovessel formation around it. The presence of deep intimal lipid accumulation was associated with reduced endothelium-dependent relaxation to substance P in isolated coronary rings. These results suggest that normal and oxidized LDLs accumulate preferably in the nutritional border zone of established DIT involving local extracellular matrix alterations but independently of inflammatory or apoptotic processes. This may contribute to the functional and morphologic abnormalities seen in human coronary atherogenesis that progresses slowly with age.

Gene expression of tropoelastin is enhanced in the aorta proximal to the coarctation in rabbits

To assess elastin biosynthesis in the aortic wall in response to acute elevation of blood pressure, we studied the aortic gene expression of tropoelastin in a rabbit midthoracic aortic coarctation model. The time points of the study were 1, 3, and 7 days and 2, 4, and 8 weeks after coarctation. Additional animals were subjected to hypercholesterolemia for analysis of tropoelastin expression in the intimal lesion. mRNA for tropoelastin was quantitated by Northern blot analysis and its distribution was revealed by in situ hybridization. The 65-kDa tropoelastin was analyzed by Western blotting and immunohistochemistry. Tropoelastin mRNA proximal to the coarctation was increased at 2 weeks and returned to baseline by 8 weeks (P < 0.05 versus control). Changes in 65-kDa tropoelastin corresponded to those of mRNA. Tropoelastin gene was expressed mainly in the intima and in the outer media at the proximal region to the stenoses, which was particularly remarkable in the intimal lesion. The results indicate that tropoelastin gene expression was enhanced in the early remodeling response to elevated blood pressure. The distribution of newly synthesized tropoelastin in the outer media suggests a reenforcement role of tropoelastin, which preserves mechanical resiliency in response to changes in tensile stress.

Arterial wall chondroitin sulfate proteoglycans: diverse molecules with distinct roles in lipoprotein retention and atherogenesis

Chondroitin sulfate proteoglycans (CSPGs) of the arterial wall are generally considered to be atherogenic because of their ability to trap cholesterol-rich lipoproteins in vitro. Nevertheless, CSPGs are a diverse group of molecules with a long evolutionary history and distinct biologic functions. The three principal CSPGs in the arterial wall are versican, which is part of the hyalectan gene family; and decorin and biglycan, which are members of a separate gene family, the small leucine-rich proteoglycans. Importantly, there is now substantial evidence that the different molecular species of CSPGs participate unequally in lipoprotein retention, and that they exert unequal regulatory effects that are related to atherogenesis. Recently available murine models with genetic manipulations that affect CSPGs now allow causal studies of the roles of these molecules to be conducted in vivo, with occasionally surprising results. Moreover, tools are being developed to examine human genetic variations that are relevant to CSPGs, which may provide additional important insights into the human disease. The era in which proteoglycans are regarded as a nondescript backdrop, playing purely nonspecific structural roles, is over. Studies in manipulated animals and in human populations will continue to reveal precise, dynamic roles for these fascinating and ancient molecules.

Oxidative modifications of LDL increase its binding to extracellular matrix from human aortic intima: influence of lesion development, lipoprotein lipase and calcium

Retention of atherogenic lipoproteins in the arterial intima by extracellular matrix (ECM) is assumed to occur during early atherogenesis and its further development. Low density lipoprotein (LDL) trapped in the intima may undergo oxidative modifications, which initiate a chain reaction in atherogenesis. Lipoprotein lipase (LPL) has been found to mediate the binding of native and oxidized LDL to ECM produced by cultured cells and to contribute to foam cell formation by mildly oxidized LDL. In this study ECM, isolated from human aortic intima with different atherosclerotic lesions, was used for the first time to measure the binding to it in vitro of native and differently oxidized 125I-LDL. Oxidation of 125I-LDL increased its binding to the ECM, which was most prominent with the material isolated from intima at the early stage of atherogenesis. With the progression of atherosclerosis, the ability of the isolated intimal ECM to bind native and oxidized 125I-LDL decreased, and strongly oxidized 125I-LDL decreased more than native and moderately oxidized 125I-LDL. LPL increased the binding of moderately oxidized 125I-LDL to the ECM more than native 125I-LDL, while it had only a small effect on strongly oxidized 125I-LDL. LPL-mediated binding of native and oxidized 125I-LDL decreased with the development of atherosclerotic lesions. Calcium ions also increased the binding of LDL to the ECM. This enhanced binding increased with the extent of LDL oxidation, especially at the early stage of atherogenesis, and decreased with lesion progression. These data suggest that the ability of ECM to retain LDL in arterial intima depends on LDL oxidation status and changes with the progression of atherogenesis. In addition, LPL and calcium ions may participate in the retention of LDL in vivo.

The influence of angiotensin-converting enzyme inhibitors on the aorta elastin metabolism in diet-induced hypercholesterolaemia in rabbits

Aortic elastin turnover is significantly accelerated in atherosclerosis, partly because of activation of the renin-angiotensin-aldosterone system caused by hypercholesterolaemia. We postulated that angiotensin-converting enzyme inhibitors (ACE-I) prevent the aortic elastin loss in experimental hypercholesterolaemia. Two doses of ACE-I (captopril, enalapril and quinapril) were used: a dose equivalent to that applied to human subjects and a dose 10 times higher. We found that the increase in serum and aortic elastolytic activity in cholesterol-fed rabbits was prevented by high-dose captopril. The elastin content in aorta homogenates from cholesterol-fed rabbits was significantly decreased. The higher dose of captopril, but no other ACE-I, prevented this decrease in aortic elastin content. In cholesterol-fed rabbits the elastin-bound calcium content was significantly elevated. The higher doses of captopril and enalapril lowered the elastin-bound calcium content. In serum and aortic homogenates of cholesterol-fed rabbits, ACE activity was elevated by 15% and 77%, respectively. Both doses of captopril, enalapril and quinapril prevented this cholesterol-induced increase in serum and aortic ACE activity. We conclude that: 1) administration of captopril at doses 10 times higher than those used in humans prevents hypercholesterolaemia increased aortic elastin loss. 2) higher doses of captopril and enalapril prevent the hypercholesterolaemia-induced increase in aortic elastin-bound calcium.

Interaction of native and modified low-density lipoproteins with extracellular matrix

Lipoprotein-matrix interactions play an important role in arterial disease. Extracellular matrix proteoglycans bind and retain specific positively charged domains on apolipoproteins B- and E-containing lipoproteins during atherogenesis. Retained lipoproteins can undergo several modifications, which may alter their interaction with extracellular matrix molecules. Growth factors, cytokines and oxidized low density lipoproteins influence proteoglycan structure, rendering them more likely to bind and retain lipoproteins during atherogenesis. Lipoproteins, native and modified, also can modulate the expression of several of the matrix degrading enzymes present in vascular tissue, thereby influencing plaque stability. Thus, the interaction of atherogenic lipoproteins with arterial wall matrix molecules can influence the genesis and progression of atherosclerosis and its complications.

An association of anti-elastin IgA antibodies with development of retinopathy in diabetic children

An important factor in the development of vascular wall alterations is degradation of the elastic fiber major protein-elastin. Elastin peptides derived from this degradation are present in the circulating blood and they are a stimulus for increased production of anti-elastin antibodies (AEAb). The aim of the present study was to examine the possible association between serum elastin AEAb and the development of diabetic vascular complications. Levels of AEAb (IgG, IgM and IgA) were determined by ELISA in sera of 28 children with Type 1 (insulin-dependent) diabetes mellitus (mean age 11.6+/-2.8 years, diabetes duration 5.1+/-2.5 years). None of the children had clinical or laboratory evidence of vascular complications. The children were followed over a period of 7 years, and 24 healthy children of similar age and sex served as a control group. During the study, four diabetics developed retinopathy, six microalbuminuria and two both retinopathy and microalbuminuria. Anti-elastin IgG showed correlation with diabetes duration (r=.48, P=.0007), HbA1c (r=.28, P=.05), triglycerides (r=.28, P=.05) and antibodies to advanced glycation endproducts (AGE) (r=.41, P=.005). Anti-elastin IgM correlated with HbA1c (r=.26, P=.038) and IgA with retinopathy (r=.32, P=.017). Our results suggest an association between the level of anti-elastin IgA antibodies and the development of diabetic retinopathy.

Oxidized low density lipoproteins regulate synthesis of monkey aortic smooth muscle cell proteoglycans that have enhanced native low density lipoprotein binding properties

Oxidized low density lipoproteins (Ox-LDL) affect several biological processes involved in atherogenesis. However, it is not known whether Ox-LDL can regulate proteoglycan expression and thus affect arterial wall lipoprotein retention. This study evaluated whether Ox-LDL, as compared with native LDL, regulates proteoglycan expression by monkey arterial smooth muscle cells in vitro and whether proteoglycans synthesized in the presence of Ox-LDL exhibit altered lipoprotein binding properties. Ox-LDL stimulated glycosaminoglycan synthesis, as measured by (35)SO(4) incorporation, by 30-50% over that of native LDL. The effect was maximal after 72 h of exposure to 5 microg/ml of Ox-LDL. The molecular sizes of versican, biglycan, and decorin increased in response to Ox-LDL, as indicated by size exclusion chromatography and SDS-polyacrylamide gel electrophoresis. These effects could be mimicked by the lipid extract of Ox-LDL. These size increases were largely due to chain elongation and not to alterations in the ratio of (35)SO(4) to [(3)H]glucosamine incorporation. Affinity chromatography indicated that Ox-LDL stimulated the synthesis of proteoglycans with high affinity for native LDL. Ox-LDL also specifically stimulated mRNA expression for biglycan (but not versican or decorin), which was correlated with increased expression of secreted biglycan. Thus, Ox-LDL may influence lipoprotein retention by regulating synthesis of biglycan and also by altering glycosaminoglycan synthesis of vascular proteoglycans so as to enhance lipoprotein binding properties.

Accumulation of co-localised unesterified cholesterol and neutral lipids within vacuolised elastin fibres in athero-prone areas of the human aorta

To investigate whether there are alterations of elastin fibres in the arterial intima at the pre-atherosclerotic stage, grossly normal areas of human thoracic aorta were taken soon after death from 13 healthy trauma victims whose ages ranged from 16 to 40 years. Two areas were compared: atherosclerosis-prone (AP) areas localised to the dorsal aspect of the aorta along the rows of intercostal branch origins, and atherosclerosis-resistant (AR) areas from the ventral aorta. Electron microscopic analysis combined with cytochemical staining was applied. Unesterified cholesterol was identified using the filipin-staining technique while neutral lipids were visualised by the OTO-technique. Intimal features were studied by combining the filipin-staining and the OTO-technique. Electron microscopical examination showed that in both AR and AP areas, some elastin fibres in the intima were vacuolised. Unesterified cholesterol was found to be predominantly localised in the musculoelastic layer, in particular, inside the vacuolised elastin fibres. This localisation was seen in all 13 AP areas studied in contrast to the AR areas where it was observed in only four of 13 aortas studied (P < 0.0005, chi2-test). Accumulation of neutral lipids inside vacuolised elastin fibres was found in five out of 13 AP areas but was not observed in any of the AR areas (P=0.01, chi2). A combination of the filipin-staining and OTO-techniques showed that some deposits of neutral lipids and unesterified cholesterol within vacuolised elastin fibres were independently located from each other, but more frequently, neutral lipids were co-located with unesterified cholesterol. The present observations indicate a difference between AP and AR intimal areas which, in particular, relates to the structure of elastin fibres in the musculoelastic layer. The observations suggest that alterations of the extracellular matrix are involved in the trapping and retention of cholesterol and neutral lipids within the intima at an early stage in the development of atherosclerotic lesions.

Aggregation of dimyristoylphosphatidylglycerol liposomes by human plasma low density lipoprotein

Turbidity (absorbance at 470 nm) measurements revealed human serum low density lipoprotein (LDL) to cause, within a few minutes and at physiological pH and [NaCl], the aggregation of liquid crystalline large unilamellar liposomes (LUVs) of dimyristoylphosphatidylglycerol (DMPG). No evidence for concomitant lipid or aqueous contents mixing was obtained with fluorescent assays for these processes, in keeping with the lack of fusion of LUVs. Involvement of apoB is implicated by the finding that tryptic digestion of LDL abrogates its ability to cause aggregation. Aggregation is not caused by VLDL, HDL2, or HDL3. Interestingly, also oxidised LDL failed to aggregate DMPG vesicles. Aggregation of DMPG LUVs by LDL did depend on the ionic strength of the medium as well as on the phase state of the lipid. More specifically, below the main transition temperature Tm maximal aggregation was seen in the presence of 25-100 mM NaCl, whereas slightly higher (up to 150 mM) [NaCl] were required when T>Tm. Aggregation due to LDL was also observed for dimyristoylphosphatidylserine as well as for dipalmitoylphosphatidylglycerol LUVs, whereas liposomes composed of either unsaturated acidic phospholipids or different phosphatidylcholines were not aggregated. Involvement of electrostatic attraction between the acidic phosphate of DMPG and cationic residues in apoB is suggested by the finding that increasing the content of dimyristoylphosphatidylcholine (DMPC) in DMPG liposomes reduced their aggregation and at XDMPC=0.50 no response was evident. Notably, increasing the mole fraction of 1-palmitoyl-2-oleyl-PG (POPG) in DMPG LUVs progressively reduced their aggregation by LDL and at XPOPG=0.50 there was complete inhibition. The latter effect of POPG is likely to be due to augmented hydration of the unsaturated lipid constituting a barrier for the contact between apoB and the vesicle surface. In keeping with this view, the presence of the strongly hygroscopic polymer, poly(ethylene glycol) at 1% (by weight) enhanced the aggregation and could partly reverse the inhibition by POPG.

Lipoprotein(a) in plasma, arterial wall, and thrombus from patients with aortic aneurysm

The plasma concentration of lipoprotein(a) [Lp(a)] is highly correlated with the incidence of cardiovascular and peripheral vascular disease. A positive physiological role for Lp(a) has not yet been clearly identified, although elevated plasma levels in pregnant women, long-distance runners, subjects given growth hormone, patients after cardiovascular surgery, and patients with cancer, diabetes, or renal disease suggest its involvement in tissue synthesis and repair. The hypothesis that Lp(a) is involved in repair/reinforcement of the aorta was tested in 38 patients undergoing surgery for aortic aneurysm. In 29 patients 1 day before surgery, the mean plasma Lp(a) protein level was 10.7 mg/dl. At about 1, 2, and 8 weeks after surgery, the level was 14.1, 15.1, and 15.2 mg/dl, respectively. These levels are significantly higher than those of a comparable group of normal subjects (6.4 mg/dl; n = 274). Specimens of resected aortic aneurysm showed extensive medial degeneration, discontinuous elastic fibers, and deposition of mucopolysaccharides; these specimens were treated with a detergent-containing buffer to extract entrapped lipoproteins. The mean Lp(a) protein level in aortic wall extracts was 14.6 ng/mg tissue; these individual values were significantly associated with plasma Lp(a) levels before surgery (r2 = 0.31, p = 0.0003). The mean Lp(a) protein level in aortic thrombus extracts was substantially higher at 69.6 ng/mg tissue; these individual levels also were significantly associated with plasma Lp(a) concentrations before surgery (r2 = 0.68, p < 0.0001). The observations that: (i) plasma Lp(a) protein is about 1.7-fold higher in patients with aortic aneurysms than in normal subjects; and (ii) that Lp(a) protein in the aneurysmic thrombus is about 4.8-fold higher than in the aortic wall suggest that this lipoprotein plays a significant and direct role in thrombus formation and in reinforcement of the aneurysmic aortic wall.

The proteoglycan decorin links low density lipoproteins with collagen type I

Decorin is a small dermatan sulfate-rich proteoglycan which binds to collagen type I in vitro and in vivo. In atherosclerotic lesions the contents of low density lipoprotein (LDL), decorin, and collagen type I are increased, and ultrastructural studies have suggested an association between LDL and collagen in the lesions. To study interactions between LDL, decorin, and collagen type I, we used solid phase systems in which LDL was coupled to a Sepharose column, or in which LDL, decorin, or collagen type I was attached to microtiter wells. The interaction between LDL and decorin in the fluid phase was evaluated using a gel mobility shift assay. We found that LDL binds to decorin by ionic interactions. After treatment with chondroitinase ABC, decorin did not bind to LDL, showing that the glycosaminoglycan side chain of decorin is essential for LDL binding. Acetylated and cyclohexanedione-treated LDL did not bind to decorin, demonstrating that both lysine and arginine residues of apoB-100 are necessary for the interaction. When collagen type I was attached to the microtiter plates, only insignificant amounts of LDL bound to the collagen. However, if decorin was first allowed to bind to the collagen, binding of LDL to the decorin-collagen complexes was over 10-fold higher than to collagen alone. Thus, decorin can link LDL with collagen type I in vitro, which suggests a novel mechanism for retention of LDL in collagen-rich areas of atherosclerotic lesions.

Intimal thickenings of human aorta contain modified reassembled lipoproteins

The aim of this study was to determine whether in human aortas early minute changes such as minimal intimal thickenings (MIT), developed in areas known to have a predilection to atherosclerosis, contain modified reassembled lipoproteins (MRLp) such as extracellular liposomes (EL) and lipid droplets (LD). These features have been previously detected in the aortic lesion-prone areas of rabbits and hamsters fed a fat-rich diet. Tissue samples of the aortic arch and thoracic aorta from 12 young subjects who died in accidents were selectively collected from grossly normal regions. By light microscopy, some of these regions were found to contain MIT. The normal areas and the MIT were separately examined by electron microscopy or subjected to fractionation and partial biochemical characterization. The MIT (approximately 25-100 microns thick) were constituted by a pronounced proliferation of extracellular matrix, especially elastin and microfibrils, with interspersed lipid deposits appearing as EL and LD. Commonly, MIT did not contain smooth muscle cells, macrophages, foam cells or cytolytic debris. Such components were only occasionally found in specimens excised from the vicinity of fatty streaks. Saline extracts of MIT or grossly normal aortic regions were subjected to a four-step purification procedure consisting of gel filtration, affinity chromatography on anti-apo B and anti-albumin Sepharose, followed by density gradient ultracentrifugation. The entire procedure was monitored by negative staining, lipid assays, SDS PAGE and immunoblotting. From the initial MRLp mixture, two fractions were obtained: fraction 1 containing multilamellar EL and LD, and fraction 2 composed mostly of unilamellar EL. As compared with serum LDL, the cholesteryl ester/unesterified cholesterol ratio was 4-6-fold lower in fraction 1 and 15-19-fold lower in fraction 2. On SDS-PAGE the fraction 2 displayed a single protein band of 66 kDa, immunochemically identified as albumin. The MRLp isolated from human aortas with minimal intimal thickenings appeared to be similar to those purified from the prelesional stage aorta of hyperlipidemic rabbits and hamsters.

Oxidized lipoproteins, altered cell function and atherosclerosis

A correlation between atherogenesis and lipoprotein oxidation was first suggested by experiments showing increased uptake by macrophages of oxidized LDL and oxidized LDL injury to cultured cells. Recent data which demonstrate the existence of oxidized lipoproteins in vivo, combined with studies showing a 'protective' effect of antioxidants against atherosclerosis progression, have greatly increased the interest in theories posing that lipoprotein oxidation is causally related to arterial disease. The fact that dozens of new compounds are produced upon the oxidation of low density lipoprotein has led, perhaps not surprisingly, to numerous discoveries in vitro of altered cell function induced by exposure of cells to oxidized LDL that are distinct from those resulting from exposure to native LDL. This brief overview will describe selected altered cell functions of oxidized lipoproteins and how they may impact on atherosclerosis.

Development of the atherosclerotic core region. Chemical and ultrastructural analysis of microdissected atherosclerotic lesions from human aorta

Lipid deposits in human atherosclerotic fibrous plaques exhibit marked differences in chemistry and ultrastructure from lipid deposits in fatty streaks, leading some investigators to question whether fibrous plaques originate from fatty streaks. To examine lesion transition, we employed lipid microanalysis, electron microscopy, and immunohistochemistry on fatty streaks, fibrolipid lesions (small raised lesions), and fibrous plaques from human aorta. Both fatty streaks and caps of fibrolipid lesions were high in esterified cholesterol content (mean, 62% of total cholesterol) and high in cholesteryl oleate content compared with cholesteryl linoleate content. Fatty streaks and fibrolipid lesion caps also showed similar morphology, characterized mostly by macrophage-derived foam cells in the superficial intima. Core lipids in both small and large raised lesions differed markedly from this pattern. Fibrolipid lesion cores showed mostly vesicular extracellular deposits, sometimes accompanied by cholesterol clefts, while fibrous plaque core deposits were also extracellular but had a variable appearance. Compared with fatty streaks, fibrolipid lesion cores showed significantly increased free/total cholesterol fractions (63%) and decreased fractional contents of cholesteryl oleate. Fibrous plaque cores had variable distributions of free and esterified cholesterol but significantly decreased cholesteryl oleate fractions compared with fatty streaks. The results support the concept of lesion transition, which is marked by deep intimal, extracellular deposition of cholesterol-rich, vesicular lipid deposits in small raised lesions. In the core region of larger raised lesions, both cholesterol-rich and cholesteryl ester-rich lipid deposits appear to form in the extracellular space.

ACE inhibition with perindopril and atherogenesis-induced structural and functional changes in minipig arteries

The effects of angiotensin-converting-enzyme (ACE) inhibition on atherosclerosis-induced changes in arterial function are unknown, as well as whether they are coupled to improvements of structural alterations in the arterial wall. An atherogenic (A) diet and the ACE inhibitor perindopril (P) were given concomitantly for 4 months to seven adult Pitman-Moore minipigs (7 months of age; A+P animals), which were compared with seven A and seven control (C) animals. Perindopril, at a daily dose of 4 mg PO that is commonly used in the clinical setting, induced a continuous 70% inhibition of serum ACE activity. At the end of the study, the atherosclerosis-induced impairment of arterial flow was investigated via the hemodynamics and vascular rheology of hindlimb arteries in non-barbiturate-anesthetized pigs. Structural alterations were evaluated from the histopathology of lesions in the arterial tree (abdominal aorta, left interventricular coronary artery [LIVCA], and brachiocephalic trunk [BCT]), with particular attention given to the analysis of the structure and composition of aortic elastic fibers. Atherosclerosis impaired the function of both capacitance and resistance arteries. Blood pressure (BP) rose significantly because of increased hindlimb peripheral resistance (HPR) and aortic input impedance (Zc), although blood flow was not affected. Altered aortic stress and elastic responses revealed that the stiffness of the aorta was markedly increased because of increased wall tension and reduced viscoelasticity, the viscous component being blunted in the arterial wall. Perindopril significantly opposed these alterations by reducing BP, HPR, and Zc and by returning parietal stiffness values to C values by increasing aortic compliance. ACE inhibition prevented the alteration of both stress and elastic responses. Major fibroproliferative fatty lesions were observed in the aorta and LIVCA, while moderate fibrosclerotic lesions were found in the BCT. Computerized densitometric analysis of orcein-stained elastin showed that elastic laminae fragmentation was prominent in the abdominal aorta, less in the LIVCA, and moderate in the BCT. Furthermore, the elastin content was reduced in the atherosclerotic aorta, although this loss of elastin was not associated with changes in the biochemical nature of alkali-insoluble elastin. Perindopril significantly prevented the development of atherosclerosis in the abdominal aorta, LIVCA, and BCT by decreasing the cross-sectional area of lesions as well as the number of lipid-laden cells in the abdominal aorta and LIVCA. In the abdominal aorta, ACE inhibition significantly prevented the alteration of elastic laminae by specifically preventing elastolytic fragmentation of dense elastic laminae, but it didn ot modify elastin content.(ABSTRACT TRUNCATED AT 400 WORDS)

Vitamin E attenuates induction of elastase-like activity by tumor necrosis factor-alpha, cholestan-3 beta,5 alpha,6 beta-triol and linoleic acid in cultured endothelial cells

Disturbances in arterial wall elastin metabolism appear to be important factors in atherosclerosis development. To evaluate this hypothesis, elastase-like activity was determined in cultured endothelial cells and their surrounding media after exposure to tumor necrosis factor-alpha (TNF), cholestan-3 beta,5 alpha,6 beta-triol (Triol) and linoleic acid (18:2). Significant increases in elastase-like activity both in the cells and in the media were observed when subconfluent endothelial cells were treated with 12 microM Triol, 500 U TNF/ml, or 90 microM 18:2, for 72 h in the presence of 5% calf serum. Even higher activities were measured when endothelial cells were seeded directly into media enriched with 18:2, TNF or Triol and treated for 72 h. Vitamin E supplementation (25 microM) attenuated elastase-like activity in cells and media, independent of treatment. These results suggest that elastase-like enzyme induction in endothelial cells may be involved in cellular perturbations induced by certain lipids and cytokines. Vitamin E may provide a protective function by preventing the induction of elastolytic enzymes. This may have implications in elastin metabolism and atherosclerosis.

Time course of 125I-labeled LDL accumulation in the healing, balloon-deendothelialized rabbit aorta

We previously showed by qualitative en face autoradiography that after 24 hours of circulation, 125I-labeled low density lipoprotein (LDL) injected in tracer amounts accumulated focally at the edges of regenerating endothelial islands in the balloon catheter-deendothelialized aorta of the normocholesterolemic rabbit. In the present study with the same animal model, we have used quantitative autoradiography to examine 125I-LDL accumulation in the healing aorta as a function of LDL circulation time from 2.5 to 40 hours. The results demonstrated that 125I-LDL accumulation in the healing aorta occurred in two kinetically and biochemically distinct compartments, one of which was in equilibrium with plasma and one of which sequestered LDL. LDL accumulation in the still-deendothelialized aorta (DEA) was diffuse and only moderately intense on autoradiography. It peaked 4 hours after injection; over the following 36 hours the disappearance of 125I-LDL from DEA paralleled the disappearance of 125I-LDL from plasma. In contrast, accumulation of 125I-LDL at the edges of regenerating endothelial islands was focal and intense. LDL accumulation in this compartment also peaked 4 hours after injection but remained elevated even at 40 hours, despite falling plasma levels of LDL. At 24 hours, edge LDL accumulation per unit area was more than five times greater than DEA accumulation. The data indicate that LDL accumulation in specific compartments of the functionally modified arterial wall occurs independently of either acute or chronic hypercholesterolemia. The contrast between labile LDL accumulation in DEA and persistent accumulation at the edges of healing aortic islands indicates that LDL accumulation in the two areas must involve different processes within the arterial wall itself.